Disabling mechanism for a combination lock

ABSTRACT

Attempts to retract the bolt of a combination lock by inserting a combination are sensed by a sensing lever and registered by a ratchet gear which drives a cam surface. Upon the registration of a predetermined number of successive unsuccessful attempts to retract the bolt, the cam surface engages the fence lever that operates the bolt and moves the fence lever to a position wherein it cannot be engaged by the tumbler means, even if the correct combination is inserted. The disabling mechanism is reset by entering a special reset combination to return the cam to its disengaged position, after which the lock will respond to the proper combination. Reset is also accomplished each time the correct combination is inserted by action of the retraction of the lock bolt.

Swaim Sept. 23, 1975 DISABLING MECHANISM FOR A COMBINATION LOCK Primary ExaminerAlbert G. Craig, Jr.

[5 7] ABSTRACT Attempts to retract the bolt of a combination lock by inserting a combination are sensed by a sensing lever and registered by a ratchet gear which drives a cam surface. Upon the registration of a predetermined number of successive unsuccessful attempts to retract the bolt, the cam surface engages the fence lever that operates the bolt and moves the fence lever to a position wherein it cannot be engaged by the tumbler means, even if the correct combination is inserted. The disabling mechanism is reset by entering a special resetcombination to return the cam to its disengaged position, after which the lock will respond to the proper combination. Reset is also accomplished each time the correct combination is inserted by action of the retraction of the 1ock-bolt.

18 Claims, 6 Drawing Figures US Patent Sept. 23,1975 Sheet 1 of5 3,906,761

US Patent Sept. 23,1975 Sheet 2 of5 3,90,761

US Patent Sept. 23,1975 Sheet 3 of5 3,906,761

lllnllIlI-Il US Patent Sept. 23,1975 Sheet 4 of5 3,6,761

US Patent Sept. 23,1975 shw 5 of5 3,906,761

DISABLING MECHANISM FOR A' COMBINATION LOCK 1 BACKGROUND or THEYIYNVENTJIOIN This invention relates generally to combination locks.

and particularly to a mechanism for disabling a combination lock in response to a predetermined number of unauthorized attempts to enter.

Combination locks provide good security against unauthorized entry because they require that a series of numbers be entered into the lock in a particular order to operate the lock. While this deters the amateur would-be lockbreaker, a knowledgable expert may be able to discover the certain characteristics of the lock, and certain key numbers, by usinghissense of feel, sight and sound, while manipulating the dial on the lock. In some types of locks, he might even learn numbers of the combination in this manner. If he is able to study the person who set the combination into the lock, he may ascertain the numbers by analyzing his birthdate, social security number, house number, or the like. Once having discovered the numbers "of the combination, the expert need only insert them in the proper sequence, and he has defeated the lock. However, even the expert, unless he is exceedingly lucky,-must try several combinations of numbers until he finds the correct combination.

The most common type of combination lock requires a three number combination, set on a dial that has at least 50 numbers. Some locks require seven numbers, and have dials ranging up to 100. Literally millions of combinations are possible on some locks. However, the expert manipulator might locate the three, or five, or seven numbers, and once having done so need only try the possible combinations on a hit-or-miss basis. When he hits the correct one, the lockis opened.

While great efforts have been made to prevent forceful defeat of combination'locks, such as by drilling and the like, little attempt has been made to prevent defeat by manipulation. My prior patent, US. Pat. No. 3,786,658, granted June 23, 1972, is directed to a device to protect combination locks from defeat by manipulation. The present invention has similar objectives, and is an improvement over the invention covered by my prior patent.

SUMMARY OF THE INVENTION A typical combination lock mechanism comprises a plurality of tumblers rotatable in sequence by-a dial knob. Each tumbler has a gate. When the proper combination is set into the lock, all of the gates are aligned,

' thus allowing a fence to drop into the gates. The fence is attached to a fence lever, which in turn is attached to the lock bolt. When the fence drops into the aligned gates, the fence lever is permitted'to move into a position where it can be engaged by an opening mechanism operated by the dial knob and tumblers, which pulls the :lever toopen the lock bolt, whether authorized or unauthorized, successful or unsuccessful. After a predetermined number of unsuccessful attempts to open the .lock have been made, the inventive mechanism disby the sensing mechanism, and registers successive unsuccessful attempts to open the lock. The fence lever disabling mechanism is engageable with the fence lever', and operates in response to the registering by the register mechanism of a predetermined number of unsuccessful attempts to open the lock. In such case, it moves the fence lever to an inoperative position where the fence willnot enter the gates, even should they be aligned, and thus the fence lever cannot be engaged to open the bolt. Quite importantly, the disabling mecha- .nism removes the fence lever from contact with the tumbler mechanism, and thus the expert cannot read the lock by feel or sound. The reset mechanism causes the register mechanism to reset to zero, at which time the fence lever alsoreturns to its operative position. The reset mechanism is actuated in two ways. The first is by dialing into the lock a special reset combination, and the second is by the bolt 'when the bolt is fully operated to open the locked door. Thus no outside force or tool is ever necessary to place the lock back in operating configuration after it has been disabled.

' The security of common combination locks is significantly improved by this-invention. Thus, in many instances, a very expensive lock can be replaced by a less expensive lock incorporating this inventive device. Since the disabling device is of add-on character and does not require modification of the existing lock mechanism, it can be adapted for use with many of .the most popular conventional combination locks.

The manner in which the invention disables a lock is such that the inability of the lock to function can be discerned only by one who knows the correct combination. Thus, it does not signal the unauthorized user to attempt physical abuse of the lock. The device resets itself automatically upon each opening of the lock, and can be reset after disabling the lock by use of the tumbler means without additional tools. It can be designed to disable after sensing any desirable number of successive unsuccessful attempts to open the lock. Finally, it is a-compact unit that is easily installed in the lock housing.

.In the following disclosureof a preferred embodiment, the invention has been described in conjunction with a type of combination lock that includes an expandable cam mechanism to operate the bolt. Other types of combination locks do not utilize an expandable cam mechanism, and in these locks the bolt is retracted by a particular additional manipulation of the dial after the combination has been entered, which arms and then operates the bolt retraction mechanism. Regardless of whatbolt retraction mechanism is used, it is within the concept of this invention to utilize this final manipulation of the dial and tumblers as a signal to the disabling system, and the sensing mechanism of the invention will be so interconnected with the tumbler means as to sense this particular manipulation.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1A is a front view, partially in section, of the inventive disabling device for a combination lock, in the inoperative position, as viewed from the rear of the combination lock in which it is installed;

FIG. 1B shows the device of FIG. 1A in the operative or disabling position;

FIG. 2 is a view taken along line 22 of FIG. 1A;

FIG. 3 is a view taken along line 3-3 of FIG 2;

FIG. 4 is 'a view taken along line 4-4 of FIG. 3; and

FIG. 5 is a close-up side view of the components of the register mechanism and the reset mechanism.

DESCRIPTION OF A PREFERRED EMBODIMENT The invention is herein described in combination with a particular type of combination lock which includes an expandable cam opening mechanism. This, however, is but one of the types with which the invention can be used. Possibly, some changes in the mechanical arrangement of the elements of the disabling device would be necessary if used with other types of combination locks, but the inventive concept would remain intact. The drawings show the elements of the invention along with the key components of a conventional combination lock, such as those used in cabinets and small safes. It should be realized that the mechanism is being viewed from the rear of the lock, as if inside the locked safe.

The combination lock with which the inventive device is used is conventional, and is only briefly described. The lock is mounted in a housing generally indicated as 12, which has a front plate 14 and side walls 16. Housing 12 would normally be located on the inside of the door of the enclosure being secured. The lock bolt 18 is slidably mounted in an opening in side wall 16 in the conventional manner, the details not being illustrated. Bolt 18 has a back face 20. Bolt 18 is caused to extend and retract by a fence lever 24. A stub shaft 26.protrudes outwardly from bolt 18, and fence lever 24 is mounted thereon, secured by a screw 27. Wrapped around stub shaft 26 is a spring 30 which biases fence lever 24 downwardly, as viewed in FIG. 1A. A fence 34 is mounted on the free end of fence lever 24, and extends outwardly perpendicularly thereto. A tooth 36 extends downwardly from the free end of a fence lever 24.

Portions of the tumbler means, in this case a three tumbler mechanism, are illustrated to the extent necessary to properly describe the invention. On the outside of the door in which the lock is installed is a dial mechanism, not shown. A shaft driven in rotation by that dial extends inwardly, through front plate 14. On the inside of housing 12 are a plurality of tumblers 38, 39 and 40. There is also the usual mechanism for engaging the tumblers as the dial is rotated clockwise and counterclockwise, but this is not shown. Each tumbler is provided with a gate 42; when all three gates are aligned, fence 34 can enter the gates, and the lock can be opened. On the end of the tumbler shaft is an expandable cam mechanism 43, which rotates with the dial. The cam mechanism comprises two fixed arcuate cam segments 44 and 46 each having a surface 48, and a pair of expandable cams 50 and 52. The expandable cams are operated between expanded and retracted positions by a separate control knob, coaxial with the dial, and also not shown. The separate control knob rotates a shaft 56 having an offset portion 58 that engages an opening 60 in expandable cam 50. A detailed explanation of this mechanism is not deemed to be necessary, for it is conventional. Suffice it to say that by rotating shaft 56, the two cam portions 50 and 52 are moved outwardly to the expanded position shown in FIG. 13. Again in the conventional manner, this clears a notch 64 for engagement by tooth 36, and thus rotation of the dial under the proper circumstances causes bolt 18 to be retracted.

Expandable cams 50 have arcuate surfaces 66. When cams 50 and 52 are retracted, surfaces 48 and 66 describe a circular surface upon which tooth 36 is supported, to hold fence 34 out of contact with the peripheries of the tumblers. Cam 50 also has a side surface 70 that is exposed when cam 50 is in the expanded position, as shown in FIG. 1B.

The disabling or restrictive manipulation device of this invention is installed in housing 12, in the space between the tumblers and bolt 18. A support plate 74 is attached to the inside of front plate 14, spaced inwardly therefrom by a spacer 75, in partially overlapping relationship with the tumblers. A shaft 76 extends from support plate 74. A cam disc 80 is rotatably mounted on the end of shaft 76, secured by a clip 82. A raised cam surface 84 extends around a portion of the periphery of cam disc 80. Cam surface 84 has a tapered leading edge 88.

Also carried by disc 80, and protruding from the opposite side, are three pins 92, 94 and 96. Pin 92 is a blocking pin, and is so aligned as to strike tumblers 38, 39, 40 under certain circumstances, explained below. Pins 94 and 96 are reset cam actuator pins and have flattened portions and 97, respectively. The operation of these pins will be explained below. Attached to disc 80 is a ratchet gear 100 having a plurality of teeth 102. A spring 104 biases cam disc 80 and ratchet gear 100 in the clockwise direction. A post 105 extends radially outwardly from ratchet gear 100, and coacts with a fixed stop 107 to define the initial position of cam 80 and ratchet gear 100. A reset cam 106 is loosely mounted on shaft 76. Reset cam 106 has a reset cam surface 108 and end surfaces 110 and 112.

As best shown in FIG. 3, a number of spring-biased pivotal levers are mounted on plate 74. A drive lever 116 has a drive pawl 118 at its free end which is engageable with teeth 102 of ratchet gear 100. At its other end, drive lever 116 is pivotally mounted on a shaft 120, which is attached to a swing lever 122, which is in turn pivotally mounted on a shaft 124 extending from support plate 74. Swing lever 122 has a flat surface 128, which is so located as to be engageable by surface 70 of expandable cam 50. A spring biases drive lever 116 counterclockwise with respect to shaft 120, and a spring 134 biases swing lever 122 counterclockwise with respect to shaft 124. A stop pin 136 limits the counterclockwise rotation of swing lever 122, and another stop pin 137 protects the mechanism from overrotation of surface 70.

A lock lever 140 is pivotally mounted on a shaft 142 extending from support plate 74. Lock lever 140 is equipped at an intermediate position with a locking pawl 144 engageable with teeth 102 and terminates at its free end in a pin 146..A spring 148 biases locklever 140 counterclockwise, into engagement withteeth 120.

A reset lever 150 is pivotally mounted at an intermediate point upon a shaft 152 attached to support plate 74. At one free end, reset lever 150 is provided with a finger 154 that is engageable with pin 146 of lock lever 140. At its other free end, reset lever 150 has a pin 156 that is engageable by back face of bolt 18.

Fence lift arm 160 is attached to fence lever 24 by screws 162. Fence lift arm 160 terminates in a follower 164 that is engageable by cam surface 84.

In discussing the operation of the lock described above, it must be appreciated that the inventive lock disabling device is an add-on device, which does not interfere with the normal operation of the lock components, unless a predetermined number of unsuccessful attempts are mode to open the lock. In the type of lock described above, a three-number combination is entered into the lock by the appropriate rotation of the dial clockwise and counterclockwise. During this portion of the operation, expandable cams 50 and 52 are in their retracted positions (FIG. 1A), and tooth 36 rests upon the rotating surfaces 48, 66 and'68. After the combination is entered, the dial is rotated to zero, and cams 50 and 52 are moved to their expanded position (FIG. 1B), thus clearing notch 64. If the correct combination has been entered, all three gates 42 will be aligned under fence 34, and fence lever 24 will be free to move downwardly so that tooth 36 can engage notch 64. Subsequent rotation of the combination dial counterclockwise as viewed causes the bolt to be pulled open.

Once cams 50 and 52 have been expanded, as the tumbler means is rotated in an attempt to retract bolt 18, surface 70 of expanded cam 50 strikes surface 128 of swing lever 122 causing drive lever 116 to move to the right, as shown in phantom in FIG. 3. This is the sensing mechanism, sensing each attempt to open the lock, whether or not it is a successful attempt. The sensing mechanism operates a register, in the form of ratchet gear 100. Movement of drive lever 116 causes drive pawl 118 to engage ratchet gear 100 and index it one step in the counterclockwise direction, against the bias of spring 104. Drive pawl 118 is subsequently retracted, but tooth 144 of lock lever 140 engages ratchet gear 100 to hold it in the new position. Ratchet gear 100 indexes each time an attempt is made to open the lock, even if the correct combination has been set.

If the correct combination has been utilized, bolt 18 will retract, and the reset mechanism will be operated, in the following manner. Back face 20 of bolt 18 contact pin 156 on reset lever 150, rotating reset lever 150 counterclockwise. Then, finger 154 strikes pin 146 on lock lever 140, rotating it clockwise, to disengage tooth 144 from ratchet gear 100. Spring 104 then 'returns the free ratchet gear 100 clockwise to its starting position.

Cam 80 rotates with ratchet gear 100, so each time ratchet gear 100 is indexed to register an attempted opening, leading edge 88 .of cam surface 84 moves closer to follower 164. At the same time, pin 92 moves closer to the peripheries of tumblers 38 39 and 40. Finally, if a predetermined number of successive unsuccessful attempts have been made, such as five, for example, cam surface 84 engages and lifts follower 164 (FIG. 1B), causing fence lever 24 to be pivoted counterclockwise about shaft 26. This lifts tooth 36 from contact with surfaces 48, 64 and 66, and will block fence lever 24 so fence 34 cannot drop into gates 42, even if the gates are properly aligned. The lock is now disabled, and will respond to no combination. Subsequent attempts to open will simply cause pin 92 to move slightly, counterclockwise, impinging each time upon the outer surface of the three tumblers.

The disabling device is equipped with a reset mechanism which is operated from outside the lock without the use of additional tools in the following manner: A second or reset combination, different from the opening combination, is set into the lock in the normal manner. This reset combination is so designed as to align gates 42 offset from fence 34, in the position shown in FIG. 1B. The reset combination is entered into the lock in the same manner as is an opening combination. Then, the dial is turned to zero and cams and 52 are expanded in the normal manner. With gates 42 positioned as shown in FIG. 13, pin 92 will no longer strike the peripheral surfaces of the, tumblers, but is free to move into gates 42 if cam 80 is indexed. Now, the dial is turned as when attempting to retract the bolt-Surface of expanded cam 50 strikes swing lever 122, ultimately moving cam one more step. This time, pin 92 is free to move into the gates 42, and therefore cam 80 can rotate. Then, surface 95 of pin 94 engages back surface 112 of reset cam 106, causing cam 106 to move counterclockwise. This causes cam surface 108 of reset cam 106 to operate upon pin 146 of lock lever 140, resulting in the camming of tooth 144 of lock lever 140 out of engagement with ratchet gear 100. Thereupon, spring 104 returns cam disc 80 and ratchet gear to their original positions. Follower 164 is freed, allowing fence lever 24 to drop downwardly to its operational position. Reset cam 106 is returned to its reset position by engagement with surface 97 of pin 96, as cam 80 nears the end of its clockwise rotation. The disabling device has now been reset, and the lock can be opened by inserting the required combination in the usual man ner. It may be desirable, depending upon the interrelationship of the various elements, to require that the device reset only after cam 80 has been indexed a number of times successively. If this be the case, then user need only cycle the dial back and forth a few degrees to successive engage and disengage surfaces 70 and 128 several times.

Perhaps, variations and modifications of the above described device may become apparent to those skilled in the art. It should therefore be understood that the invention is not limited to the exact device described herein, but its scope is governed only by the appended claims.

I claim:

1. A disabling device for improving the security of a combination lock of the type having tumbler means including gates and a fence movable into said gates when the proper combination has been entered into said lock, and a fence lever operable by a particular manipulation of said tumbler means to operate a lock bolt or the like to open said lock, said device comprising:

sensing means operable by said tumbler means for sensing each said particular manipulation of said tumbler means and thereby each attempt to open said lock,

register means operated by said sensing means for registering successive of said particular manipulations which result in unsuccessful attempts to open said lock,

fence lever disabling means operated by said register means for disabling said fence lever when a predetermined number of successive of said particular manipulations which result in unsuccessful attempts to open said lock have been registered by said register means, and

reset means operated by said tumbler means for resetting said register means and said fence lever disabling means so that said fence lever is again rendered operable and said lock can respond to the proper combination.

2. The device of claim 1 wherein said fence lever normally is in contact with said tumbler means, and wherein said fence lever disabling means moves said fence lever out of contact with said tumbler means when said fence lever disabling means is operated by said register means.

3. The device of claim 2 wherein said tumbler means comprises a rotatable portion having an outer surface, said fence lever normally contacting said outside surface, and wherein said fence lever disabling means holds said fence lever spaced from said outside surface.

4. The device of claim 1 wherein said register means comprises a ratchet gear and a ratchet drive means engageable with said ratchet gear and driven by said sensing means to move said ratchet gear step-by-step in response to said sensing means.

5. The device of claim 1 wherein said disabling means comprises means for preventing said fence from entering said gates.

6. The device of claim 1 wherein said reset means is also operated by said lock bolt or the like each time said lock bolt is retracted.

7. The device of claim 1 wherein said disabling means comprises cam means engageable with said fence lever to move said fence lever from an operating position wherein said fence can engage said gates and a disabled position wherein said fence cannot engage said gates, said cam means being movable by said register means.

8. The device of claim 7 wherein said sensing means comprises a sensing lever engageable by said tumbler means and connected to said drive lever.

9. The device of claim 7 wherein said cam means comprises a cam surface rotatable into engagement with said fence lever, and wherein said register means comprises a ratchet gear attached to said cam means and rotatable step-by-step by a ratchet drive lever operated by said sensing means, said cam surface being moved into engagement with said fence lever when said predetermined number of successive of said particular manipulations which result in unsuccessful attempts has been sensed, and ratchet locking means to hold said ratchet in the position driven by said drive lever.

10. The device of claim 9 wherein said reset means comprises a first reset mechanism for disengaging said ratchet locking means from said ratchet, said first reset mechanism comprising a first reset lever engageable with said ratchet locking means to release said ratchet locking means, said first reset lever being operated by said lock bolt each time said lock is successfully opened.

11. The device of claim 10 wherein said register means further comprises can means movement limiting means engageable with the periphery of said tumbler means to arrest the movement of said cam means at a limiting position when said cam surface has engaged said fence arm, wherein said reset means further comprises a second reset mechanism for disengaging said ratchet locking means when a reset combination has been entered into said lock and said particular manipulation of said tumbler means is performed, said reset combination aligning said gates with said cam means movement limiting means so that said cam means can be moved beyond such limiting position, said particular manipulation then moving said cam means beyond said limiting position and operating said second reset mechanism.

12. The device of claim 11 wherein said second reset mechanism comprises a second rotatable cam engageable with said ratchet lock lever and driven by said ratchet gear when said cam surface has moved past said limiting position.

13. The device of claim 1 wherein said tumbler means further comprises radially movable expandable cam means and said predetermined manipulation causes said expandable cam means to move radially outwardly from a retracted position to an expanded position wherein said fence lever can engage said tumbler means to operate said lock bolt, said sensing means and said reset means being operated by said expandable cam means.

14. The device of claim 13 wherein said sensing means comprises a sensing lever engageable by said expandable cam means when said expandable cam means is in said expanded position, said sensing lever being movable between a rest position and an operating position,

wherein said register means comprises a ratchet gear and a ratchet drive lever connectable to said sensing lever and driven thereby to index said ratchet gear step-by-step in response to said sensing means,

wherein said disabling means comprises cam means engageable with said fence lever to move said fence lever from an operating position wherein said fence can engage said gates and a disabled position wherein said fence cannot engage said gates, said cam means being movable by said register means, and

wherein said reset means comprises a reset cam movable by action of said expandable cam means when said expandable cam means is in said expanded position.

15. The device of claim 14 wherein said cam means is rotatable into engagement with said fence lever, and wherein said ratchet gear and said cam means are connected and are coaxial.

16. A method of operating a combination lock of the type having tumbler means including gates and a fence movable into said gates when the proper combination has been entered into said lock and a fence lever operable by a particular manipulation of said tumbler means to operate a lock bolt or the like, said method comprissensing each said particular manipulation of said tumbler means,

registering successive of said particular manipulations of said tumbler means which do not result in successful opening of said bolt means or the like,

disabling said fence lever upon the registration of a predetermined number of said successive of said particular manipulations that do not result in sucmanipulations of said tumbler means by entering said reset combination and performing said particular manipulation.

18. The method of claim 16 further comprising the step of clearing prior registrations of said particular manipulations by successfully opening said bolt means or the like. 

1. A disabling device for improving the security of a combination lock of the type having tumbler means including gates and a fence movable into said gates when the proper combination has been entered into said lock, and a fence lever operable by a particular manipulation of said tumbler means to operate a lock bolt or the like to open said lock, said device comprising: sensing means operable by said tumbler means for sensing each said particular manipulation of said tumbler means and thereby each attempt to open said lock, register means operated by said sensing means for registering successive of said particular manipulations which result in unsuccessful attempts to open said lock, fence lever disabling means operated by said register means for disabling said fence lever when a predetermined number of successive of said particular manipulations which result in unsuccessful attempts to open said lock have been registered by said register means, and reset means operated by said tumbler means for resetting said register means and said fence lever disabling means so that said fence lever is again rendered operable and said lock can respond to the proper combination.
 2. The device of claim 1 wherein said fence lever normally is in contact with said tumbler means, and wherein said fence lever disabling means moves said fence lever out of contact with said tumbler means when said fence lever disabling means is operated by said register means.
 3. The device of claim 2 wherein said tumbler means comprises a rotatable portion having an outer surface, said fence lever normally contacting said outside surface, and wherein said fence lever disabling means holds said fence lever spaced from said outside surface.
 4. The device of claim 1 wherein said register means comprises a ratchet gear and a ratchet drive means engageable with said ratchet gear and driven by said sensing means to move said ratchet gear step-by-step in response to said sensing means.
 5. The device of claim 1 wherein said disabling means comprises means for preventing said fence from entering said gates.
 6. The device of claim 1 wherein said reset means is also operated by said lock bolt or the like each time said lock bolt is retracted.
 7. The device of claim 1 wherein said disabling means comprises cam means engageable with said fence lever to move said fence lever from an operating position wherein said fence can engage said gates and a disabled position wherein said fence cannot engage said gates, said cam means being movable by said register means.
 8. The device of claim 7 wherein said sensing means comprises a sensing lever engageable by said tumbler means and connected to said drive lever.
 9. The device of claim 7 wherein said cam means comprises a cam surface rotatable into engagement with said fence lever, and wherein said register Means comprises a ratchet gear attached to said cam means and rotatable step-by-step by a ratchet drive lever operated by said sensing means, said cam surface being moved into engagement with said fence lever when said predetermined number of successive of said particular manipulations which result in unsuccessful attempts has been sensed, and ratchet locking means to hold said ratchet in the position driven by said drive lever.
 10. The device of claim 9 wherein said reset means comprises a first reset mechanism for disengaging said ratchet locking means from said ratchet, said first reset mechanism comprising a first reset lever engageable with said ratchet locking means to release said ratchet locking means, said first reset lever being operated by said lock bolt each time said lock is successfully opened.
 11. The device of claim 10 wherein said register means further comprises can means movement limiting means engageable with the periphery of said tumbler means to arrest the movement of said cam means at a limiting position when said cam surface has engaged said fence arm, wherein said reset means further comprises a second reset mechanism for disengaging said ratchet locking means when a reset combination has been entered into said lock and said particular manipulation of said tumbler means is performed, said reset combination aligning said gates with said cam means movement limiting means so that said cam means can be moved beyond such limiting position, said particular manipulation then moving said cam means beyond said limiting position and operating said second reset mechanism.
 12. The device of claim 11 wherein said second reset mechanism comprises a second rotatable cam engageable with said ratchet lock lever and driven by said ratchet gear when said cam surface has moved past said limiting position.
 13. The device of claim 1 wherein said tumbler means further comprises radially movable expandable cam means and said predetermined manipulation causes said expandable cam means to move radially outwardly from a retracted position to an expanded position wherein said fence lever can engage said tumbler means to operate said lock bolt, said sensing means and said reset means being operated by said expandable cam means.
 14. The device of claim 13 wherein said sensing means comprises a sensing lever engageable by said expandable cam means when said expandable cam means is in said expanded position, said sensing lever being movable between a rest position and an operating position, wherein said register means comprises a ratchet gear and a ratchet drive lever connectable to said sensing lever and driven thereby to index said ratchet gear step-by-step in response to said sensing means, wherein said disabling means comprises cam means engageable with said fence lever to move said fence lever from an operating position wherein said fence can engage said gates and a disabled position wherein said fence cannot engage said gates, said cam means being movable by said register means, and wherein said reset means comprises a reset cam movable by action of said expandable cam means when said expandable cam means is in said expanded position.
 15. The device of claim 14 wherein said cam means is rotatable into engagement with said fence lever, and wherein said ratchet gear and said cam means are connected and are coaxial.
 16. A method of operating a combination lock of the type having tumbler means including gates and a fence movable into said gates when the proper combination has been entered into said lock and a fence lever operable by a particular manipulation of said tumbler means to operate a lock bolt or the like, said method comprising: sensing each said particular manipulation of said tumbler means, registering successive of said particular manipulations of said tumbler means which do not result in successful opening of said bolt means or the like, disabling said fence lever upon the registration of a predetermined number of sAid successive of said particular manipulations that do not result in successful opening of said bolt means or the like, whereby said lock cannot be opened, entering a reset combination into said tumbler means to prepare to enable said fence lever, and enabling said fence lever by performing said particular manipulation of said tumbler means after said reset combination has been entered.
 17. The method of claim 16 further comprising the step of clearing prior registrations of said particular manipulations of said tumbler means by entering said reset combination and performing said particular manipulation.
 18. The method of claim 16 further comprising the step of clearing prior registrations of said particular manipulations by successfully opening said bolt means or the like. 